The Arctic Belt is the northernmost geographic belt of the Earth, including most of the Arctic. The border of the Arctic belt is usually drawn along the isotherm 5o From the warmest month (July or August).
The Arctic belt is characterized by negative or small positive values of the radiation balance, the dominance of the Arctic, long polar night, low and surface oceanic waters. The seas of the Arctic belt are characterized by stable ice cover.
On land, the arctic belt includes the arctic desert zone. The flora is poor, has a mosaic distribution. The life of animals (polar bears, walruses, seals) is associated with the sea. Birds nest on the islands in summer.
The Antarctic belt is the southern natural geographic belt of the Earth, including Antarctica with adjacent islands and the ocean waters washing it.
Usually, the border of the Antarctic belt is drawn along the 5o isotherm from the warmest month (January or February).
The Antarctic belt is characterized by: negative values of the radiation balance, Antarctic with low air temperatures, long polar night, significant ocean ice coverage.
Antarctic deserts prevail on land. In the oases and on most of the islands, there is moss and lichen vegetation. The animal world is not rich.
The Subarctic Belt is a natural geographic belt in the Northern Hemisphere between the Arctic belt in the north and the temperate belt in the south. The subarctic belt includes tundra and forest-tundra zones.
The subarctic zone has a cold climate; most of atmospheric precipitation falls in solid form, the snow cover lasts 7-8 months. Permafrost and associated forms are characteristic of the subarctic belt.
The tundra zone is a natural land area, mainly in the Northern Hemisphere between the zones of forest-tundra and arctic deserts in Russia, Canada and the USA (Alaska). Tundra zones are characterized by strong swampiness, wide distribution, tundra-gley soils. The vegetation cover is dominated by lichens, mosses, low-growing grasses, shrubs and shrubs. In the summer, a huge number of migratory birds fly to the tundra. Both birds and animals are awake for a significant part of the day in conditions of a long polar day. In winter, birds leave the tundra, animals migrate to more southern regions. Some inhabitants of the tundra, for example, lemengi rodents, spend the winter under, many animals have warm fur.
Temperate zones - geographic zones of the Earth located in temperate latitudes:
- in the Northern Hemisphere - between the subarctic and subtropical belts: from 65o N. up to 40o N;
- in the Southern Hemisphere - between the subantarctic and subtropical belts: from 58o S. up to 42o S
The temperate zones are characterized by a clear seasonality of the thermal regime with a long snowy winter with the formation of a snow cover on land and a significant weakening or termination of plant vegetation in winter.
In the natural landscapes of temperate zones in Eurasia, coniferous, mixed and deciduous forests, forest-steppe, steppe, semi-desert and desert are successively replaced from north to south.
In the taiga, conifers have adapted to harsh conditions - they can withstand prolonged cold and lack of water. The taiga forest has more favorable conditions for the life of animals in comparison with the tundra. There are many fur animals.
The mixed forest zone is transitional between coniferous and deciduous forests. It is characterized by a combination of broad-leaved, small-leaved and coniferous trees.
A special zone is represented by the monsoon forests of the Far East, which are distinguished by a variety of flora, an abundance of vines and layering.
Deciduous forests are formed by trees with falling leaves. The forests have varied undergrowth and dense grass. There are many ungulates, animals, birds, leaf-eating insects.
Steppes are herbaceous communities, represented by grasses with an admixture of heavily pubescent dicotyledonous plants. Nowadays most of the territory steppe zones the temperate zone is plowed up. Steppe is the habitat of ungulates, rodents, predators, birds nesting on the ground.
Subtropical zones - natural geographic zones of the Northern and Southern Hemispheres, approximately between 30o and 40o N. and south latitude, between temperate and tropical zones. The subtropical zones are dominated by a subtropical climate.
The subtropical zones are distinguished by the alternation of moderate (in winter) and tropical (in summer) air masses, which determine different temperatures and humidity. Thermal conditions allow year-round vegetation of plants.
Within the land of the Northern Hemisphere, the amount of atmospheric precipitation and their regime change significantly from oceanic regions to inland regions, which, combined with an increase in the continentality of the climate in the same direction, determines significant landscape differences and the formation of:
- zones of subtropical evergreen forests and shrubs (Mediterranean zone);
- zones of subtropical monsoon mixed forests;
- forest-steppe zones;
- zones of subtropical steppes;
- subtropical semi-deserts;
- subtropical deserts.
Mediterranean hard-leaved forests and shrubs are common in areas where temperatures in winter can drop to + 10o- + 5oC, but frost, as a rule, does not happen. This area is characterized by evergreen trees, a variety of conifers, shrubs with hard leathery leaves that secrete essential oils.
Tropical zones - natural geographic zones of the Northern and Southern Hemispheres, mainly from 20o to 30o N. and y.sh. between the subtropical and subequatorial belts.
The tropical zones are characterized by the predominance of trade wind circulation, which contributes to the formation of a hot and dry tropical climate. In tropical zones, temperatures are constantly high, with less than 200 mm of precipitation per year. Wet and dry seasons are distinguished in the eastern sectors of the continents.
On land, semi-deserts and deserts prevail, in more humid places, savannas and deciduous forests prevail.
Semi-desert zones are natural zones in which natural landscapes are dominated by semi-deserts. Semi-desert zones occupy an intermediate position:
- between zones of deserts and steppes in temperate and subtropical zones;
- between zones of deserts and savannas in the tropical zone.
Semi-arid zones are common on all continents, except for Antarctica, mainly in the western oceanic and inland sectors.
Semi-desert zones are characterized by a dry continental climate with an annual precipitation usually not exceeding 300 mm. Surface runoff is small, rivers usually dry up in dry seasons. The vegetation of semi-desert zones is usually sparse, with a predominance of grass-wormwood communities, perennial grasses and shrubs.
Semi-desert zones are common in the temperate zone of the Northern Hemisphere, subtropical and tropical zones of the Northern and Southern Hemispheres.
Desert zones are natural zones in which natural landscapes are dominated by deserts. Distributed in the temperate zone of the Northern Hemisphere, subtropical and tropical zones of the Northern and Southern Hemispheres.
In desert zones, the climate is extremely dry, with annual precipitation below 200-250 mm. Vegetation - herbaceous and dwarf shrubs, sparse, covers only a small part of the surface, in the most arid conditions it is practically absent. Plants have a variety of moisture-saving devices. Many ephemeroids are plants with a short growing season. Among the animals there are many nocturnal and twilight species, which spend all the hot time in burrows and shelters. Some desert dwellers have a brisk run for long distances.
Zones of tropical forests - natural zones of the eastern sectors of the continents within the tropical zones of the Northern and Southern Hemispheres with a predominance of tropical forests in the landscapes.
Tropical rainforest zones are common in southern Florida, the West Indies, Central and South America, the Indochina Peninsula, Madagascar Island, Australia, the islands of Oceania and the Malay Archipelago; occupy mainly the windward slopes of mountainous areas. The climate is tropical humid or seasonally humid with a predominance of humid oceanic trade winds. The subzone of permanently moist forests is dominated by evergreen forests with exceptional species diversity on red-yellow lateritic soils. The zones of tropical forests are characterized by a thick weathering crust, intense runoff; in the subzone of seasonally moist forests, along with evergreen forests, deciduous forests on red ferallite soils are widespread.
Subequatorial belts are natural geographic belts of the Northern and Southern Hemispheres between the equatorial and tropical zones. The climate of the subequatorial zones is characterized by the dominance of equatorial monsoons with dry winters and humid summers, constantly high temperatures. On land, there are zones of savannas and woodlands and subequatorial monsoon mixed forests.
Savannah zones are natural zones, mainly in subequatorial zones, less often in tropical and subtropical zones. Widely distributed in Africa (40% of the territory), there are in South and Central America, Asia, Australia. The climate is seasonally humid, with a clear change between dry and rainy periods.
In the savannah zones, the duration of the rainy period ranges from 8-9 months (at the equatorial borders of the zones) to 2-3 months (at the outer borders). Parallel to the decrease in annual precipitation, the vegetation cover is changing from tall-grass savannas and savanna forests on red soils to deserted savannas, xerophilic open forests and shrubs on brown-red and red-brown soils. The abundance of plant food brings with it a variety of herbivores and a variety of carnivores. The alternation of wet and dry periods causes seasonal migrations of animals.
Subequatorial monsoon forest zones are natural subequatorial zones in Central and South America, Africa, southern Asia and northeastern Australia. In these zones, the climate is characterized by the dominance of equatorial monsoons. The dry season lasts 2.5-4.5 months. The soils are red-colored lateritic.
Equatorial belt - the geographic belt of the Earth, located on both sides of the equator: from 5o - 8o N. up to 4o - 11o S The equatorial belt is characterized by a constantly hot and humid equatorial climate, due to a large inflow. Climatic seasons are not expressed or weakly expressed. Equatorial forests are characterized by large species diversity, multi-tiered, lack of shrubs and grasses. The trees are evergreen, bloom and bear fruit all year round. Many animals spend their entire lives among the branches of trees. On the surface of the soil, either very small animals can live, or large ones, easily making their way among the dense forest thickets.
Site search.
Despite the fact that its very name "desert" comes from words such as "empty", "emptiness", this amazing natural object is filled with diverse life. The desert is very diverse: in addition to the sand dunes that our eyes habitually draws, there are saline, stony, clayey, as well as snowy deserts of Antarctica and the Arctic. Taking into account the snowy deserts, this natural zone belongs to one fifth of the entire surface of the Earth!
Geographic object. The meaning of deserts
home distinctive feature deserts are drought. The reliefs of the deserts are very diverse: island mountains and complex highlands, small hills and bedded plains, lake depressions and dried up centuries-old river valleys. The formation of the relief of deserts is greatly influenced by the wind.
Man uses the deserts as pastures for livestock and areas for the cultivation of some cultivated plants. Plants for livestock thrive in the desert thanks to the horizon of condensed moisture in the soil, and desert oases, bathed in sun and fed by water, are extremely favorable places for growing cotton, melons, grapes, peach and apricot trees. Of course, for human activity only small areas of deserts are suitable.
Desert characteristics
Deserts are located either next to the mountains, or almost on the border with them. High mountains hinder the movement of cyclones, and most of the precipitation they bring falls in the mountains or foothill valleys on one side, and on the other side - where the deserts lie - only small remnants of rain reach. The water that manages to reach the desert soil flows down surface and underground streams, collecting in springs and forming oases.
Deserts are characterized by various amazing phenomena that are not found in any other natural zone. For example, when there is no wind in the desert, the smallest grains of dust rise into the air, forming the so-called "dry fog". Sandy deserts know how to "sing": the movement of large layers of sand generates a high and loud, slightly metallic sound ("singing sands"). Deserts are also known for their mirages and terrible sandstorms.
Natural areas and types of deserts
Depending on the natural zones and the type of surface, there are the following types of deserts:
- Sandy and sandy-crushed stone... They are very diverse: from chains of dunes devoid of any vegetation, to areas covered with shrubs and grass. Getting around in the sandy desert is extremely difficult. Sands do not occupy most of the deserts. For example: the sands of the Sahara make up 10% of its territory.
- Stony (hamadas), gypsum, gravelly and gravelly-pebble... They are combined into one group according to the characteristic feature - a rough, hard surface. This type of desert is the most widespread on the globe (the hamads of the Sahara occupy 70% of its territory). Succulents and lichens grow in tropical rocky deserts.
- Saline... In them, the concentration of salts prevails over other elements. Salt deserts can be covered with a hard cracked salt crust or salt bog that can completely suck in a large animal and even a person.
- Clayey... Covered with a smooth clay layer stretching for many kilometers. They are characterized by low mobility and low water properties(The surface layers absorb moisture, preventing it from penetrating deep, and dry quickly during the heat).
Desert climate
Deserts occupy the following climatic zones:
- moderate (Northern Hemisphere)
- subtropical (both hemispheres of the Earth);
- tropical (both hemispheres);
- polar (icy deserts).
The deserts are dominated by a continental climate (very hot summers and Cold winter). Precipitation is extremely rare: from once a month to once in several years and only in the form of showers, because small precipitation does not reach the ground, evaporating in the air.
Daily temperature in a given climatic zone very fluctuates: from +50 o C during the day to 0 o C at night (tropics and subtropics) and up to -40 o C (northern deserts). The air of the deserts is particularly dry: from 5 to 20% during the day and from 20 to 60% at night.
The largest deserts in the world
Sahara or Queen of the Deserts- the largest desert in the world (among hot deserts), the territory of which covers over 9,000,000 km 2. Located in North Africa, it is famous for its mirages, which happen here on average 150 thousand per year.
Arabian Desert(2,330,000 km 2). It is located on the territory of the Arabian Peninsula, also capturing part of the land of Egypt, Iraq, Syria, Jordan. One of the most capricious deserts in the world, known for particularly sharp fluctuations in daily temperature, strong winds and dust storms. From Botswana and Namibia to South Africa stretches over 600,000 km 2 Kalahari, constantly increasing its territory due to alluvium.
Gobi(more than 1,200,000 km 2). It is located in the territories of Mongolia and China and is the largest desert in Asia. Clay and stony soils occupy almost the entire territory of the desert. On South Central Asia lie Karakum("Black Sands"), occupying an area of 350,000 km 2.
Victoria Desert- occupies almost half of the Australian continent (over 640,000 km 2). Famous for its red sand dunes, as well as a combination of sandy and rocky areas. Also located in Australia Great Sandy Desert(400,000 km 2).
Two South American deserts are very noteworthy: Atacama(140,000 km 2), which is considered the driest place on the planet, and Salar de Uyuni(more than 10,000 km 2) is the largest salt desert in the world, with more than 10 billion tons of salt reserves.
Finally, the absolute champion in terms of occupied territory among all world deserts is Icy desert Antarctica(about 14,000,000 km 2).
http: //www..jpg "align = left> The Arctic Desert is part of the Arctic geographic zone, located in the high latitudes of the Arctic. The Arctic Desert Zone - the northernmost of the natural zones - is located in the high latitudes of the Arctic. Its southern border is located at about 71 parallels (Wrangel Island). The zone of arctic deserts extends to approximately 81 ° 45 "N. NS. (islands of the Franz Josef Land archipelago). The Arctic Desert Zone includes all islands in the Arctic Basin: this is the island of Greenland,northern part of the Canadian archipelago,Svalbard archipelago, islands of Franz Josef Land archipelago, Severnaya Zemlya, New earth, New Siberian Islandsand a narrow strip along the coast of the North Arctic Ocean within the Yamal, Gydansky, Taimyr, Chukotsky peninsulas). These spaces are covered with glaciers, snow, rubble and debris.
Arctic Desert Climate
http: //www..ru) .jpg "align = right> The climate is arctic, with long and harsh winters, summers are short and cold. There are no transitional seasons in the Arctic desert. During the polar night it is winter, and during the polar day - summer The polar night lasts 98 days at 75 ° N lat., 127 days - at 80 ° N lat. Average winter temperatures are -10 to -35 °, dropping to -60 °. Frost weathering is very intense.
The air temperature in summer is slightly above 0 ° С. The sky is often covered with gray clouds, it is raining (often with snow), thick fogs are formed due to the strong evaporation of water from the ocean surface.
Even on the "southern" island of the Arctic Desert - Wrangel Island - according to eyewitnesses, there is no autumn, winter comes immediately after the short Arctic summer. The wind changes to the north and winter comes overnight.
The Arctic climate is shaped not only by low temperatures at high latitudes, but also by the reflection of heat from snow and ice crust. Ice and snow cover lasts about 300 days a year.
The annual amount of precipitation is up to 400 mm. The soils are saturated with snow and barely thawed ice.
Vegetation cover
http: //www..jpg "align = left> The main difference between the desert and the tundra is that it is possible to live in the tundra by feeding on its gifts, but in the Arctic desert it is impossible to do this. That is why there was no indigenous population on the territory of the Arctic islands.
The territory of the Arctic deserts has open vegetation, which covers about half of the surface. The desert is devoid of trees and bushes. There are small isolated areas with crustose lichens on rocks, mosses, various algae on stony soils and herbaceous vegetation - sedges and grasses. In the conditions of the Arctic desert, there are some types of flowering plants: polar poppy, crumble, stellate, alpine foxtail, arctic pike, bluegrass, buttercup, saxifrage, etc. These islets of vegetation look like oases among endless ice and snow.
The soils are shallow, with an insular distribution, mainly under vegetation. Spaces free from glaciers are bound by permafrost, the thawing depth does not exceed 30-40 cm even under polar day conditions. The processes of soil formation are carried out in a thin active layer and are located on initial stage development.
The upper part of the soil profile is characterized by the accumulation of iron and manganese oxides. Ferruginous-manganese films are formed on the rock fragments, which determines the brown color of the polar desert soils. On the coastal areas saline by the sea, polar desert saline soils are formed.
There are practically no large stones in the Arctic desert. Mostly sand and small flat cobblestones. There are globular nodules, which are composed of silicon and sandstone, from a few centimeters to several meters in diameter. The most famous nodules are spherulites on Champa Island (FFI). Every tourist considers it his duty to take a photo with these balloons.
Animal world
http: //www..jpg "align = right> Due to the sparse vegetation, the fauna of the Arctic deserts is relatively poor. Terrestrial fauna is poor: arctic wolf, arctic fox, lemming, New Zealand deer, in Greenland - a musk ox. On the coast you can find pinnipeds: walruses and seals.
Polar bears are considered the main symbol of the Arctic. They lead a semi-aquatic life; the key areas of land for the breeding of polar bears are the northern coast of Chukotka, Franz Josef Land, Cape Zhelaniya on Novaya Zemlya. There are about 400 ancestral dens on the territory of the Wrangel Island reserve, therefore it is called the bear's maternity hospital.
http: //www..jpg "align = left> The most numerous inhabitants of the harsh northern region are birds. These are guillemots, puffins, eiders, rose gulls, snowy owls, etc. Seabirds nest on the rocky shores in summer, forming“ bird colonies ” The largest and most diverse seabird colony in the Arctic nests on Rubini Rock, which is located in the ice-free Tikhaya Bay off Hooker Island (FFI), which has up to 18,000 guillemots, guillemots, kittiwakes and other seabirds.
INTRODUCTION
About 20 million sq. km. the surface of the globe is occupied by deserts, where many natural phenomena are still a mystery. Deserts are extremely arid areas of the globe that are poor in water and vegetation. According to UNESCO, deserts make up 23% of the area of all continents.
Most of the world's deserts were formed on geological platforms and occupy the most ancient land areas. Deserts in Asia, Africa and Australia are usually located at an altitude of 200 to 600 m above sea level, in Central Africa and North America - at an altitude of 1,000 m above sea level.
Deserts leave a deep imprint on the face of the African continent. In Africa, almost the entire northern part of the continent belongs to deserts, from 12-15о N. to the shores of the Mediterranean Sea. The largest desert in South Africa, the Namib, stretches from the Atlantic coast to the southeast along the Orange River Valley. In the central part of the mainland lies the rocky semi-desert Kalahari.
Most of the world's deserts were formed on geological platforms and occupy the most ancient land areas. Deserts in Asia, Africa and Australia are usually located at altitudes of 200-600 m above sea level, in Central Africa and North America - at an altitude of 1,000 m above sea level. Deserts are one of the landscapes of the Earth, which arose just as naturally as all others, thanks, first of all, to the peculiar distribution of heat and moisture over the earth's surface and the associated development of organic life, the formation of biogeocenotic systems. A desert is a certain geographic phenomenon, a landscape that lives its own special life, has its own laws, which, during development or degradation, has its inherent features, forms of change.
The object of the course work is the deserts of Africa.
The subject of the course work is the physical and geographical characteristics of the African deserts.
The purpose of this work is to consider issues related to the physical and geographical characteristics of the African deserts.
Based on the set goal, it is necessary to solve the following tasks:
To give a general overview of the natural features of the deserts of Africa.
Describe the results of development natural resources deserts of Africa.
Consider the patterns of formation and distribution of deserts.
Consider the geographical features of deserts.
CHAPTER 1. MAIN CHARACTERISTIC DESERT
.1 Definition and Geographical Features of Deserts
Desert is a zonal type of landscape that has developed under conditions of moisture deficit (arid desert) or heat (cold desert) and is characterized by very sparse and depleted phytocenoses (a set of plants). Deserts are common in the temperate zone of the Northern Hemisphere, subtropical and tropical zones of the Northern and Southern Hemispheres.
A desert is a certain geographic phenomenon, a landscape that lives its own special life, has its own laws, which, during development or degradation, has its inherent features, forms of change. Deserted lands (even reclaimed ones) retain their differences from pasture, irrigated and industrialized territories. Within each of them there are also differences.
Arid deserts are distinguished by high summer seasonal (or even annual) air temperatures, low annual precipitation (usually from 100 to 200 mm.), Lack of surface runoff, salinity groundwater, uneven amount of precipitation. It is in the desert that the following are observed: the absolute minimum of annual precipitation (from 0 to 10-15 mm.); the absolute maximum air temperature (59 ° С), heating of the soil surface to 80 ° С, decrease in the relative humidity of the air to 5-10%.
In the desert, the features of aridity (aridity) are expressed in the sharpest form and reach the extreme, beyond which begins the complete destruction of the biological life of the landscape and the loss of economic potential, the transition to an extra-arid state (where the probability of permanent droughts is 75-100%).
A cold desert is a type of desert in which the scarcity of vegetation is mainly due to low temperatures. At the same time, ice and high-mountain deserts are distinguished. Snow deserts are distinguished separately (in Antarctica and the Arctic - the Arctic desert). The territory of deserts, as a rule, is without drainage, sometimes they are crossed by transit rivers (Syr Darya, Amu Darya, Nile, Yellow River, etc.); there are many drying up lakes and rivers, often changing their shape and size (Lobnor, Chad, Eyr), periodically drying up streams are characteristic.
Groundwater is often mineralized. The soils are poorly developed, characterized by the predominance of water-soluble salts in the soil solution over organic substances, salt crusts are common.
Deserts have existed since ancient geological times and have a long evolutionary history. As a result of the periodic change in the Earth's climates, the boundaries of desert territories also changed. Most of the world's deserts were formed on ancient platforms, and occupy the most ancient land areas.
Deserts in Asia, Africa and Australia are usually located at an altitude of 200 to 600 m, in Central Africa and North America - at an altitude of 1000 m above sea level, within the ancient river, delta and lake boundaries. They often occupy areas of foothill troughs or intermontane depressions (depressions). Some deserts were formed on the site of large lakes of the Quaternary period. Surface deposits of the desert are associated with the geological structure of the territory and exogenous processes - Quaternary and modern (stony and gravelly eluvium on Paleogene-Neogene and Cretaceous conglomerates; pebble, sandy or loamy-clayey proluvial deposits of foothill plains; sandy, ancient riverine sands. The relief is low-mountainous, hummocks, plains (alluvial and proluvial), large lacustrine depressions. In other deserts, sand massifs arose in arid conditions due to the scattering of gneisses, quartzites and other metamorphic rocks or sedimentary rocks of the Cretaceous and Jurassic ages. In the temperate zone, conditions for the formation of deserts occur in inland regions such as Central Asia, where the amount of precipitation does not exceed 200 mm.
1.2 Formation of deserts
Deserts are one of the landscapes of the Earth, which arose just as naturally as all others, due primarily to the peculiar distribution of heat and moisture over the earth's surface and the associated development of organic life, the formation of biogeocenotic systems. This understanding of the desert - as a certain landscape with its inherent features and properties of nature, which arose in certain latitudes of the Earth - does not cause serious disagreements in the scientific literature. Disputes, if they do arise, are about the main indicators of deserts - climatic, botanical, etc. The very concept of "desert" in the genetic sense and as a certain system of geobiocenosis is perceived unambiguously.
The process of formation and development of deserts is based, first of all, on the uneven distribution of heat and moisture on the Earth, the zoning of the geographic envelope of our planet. The zonal distribution of temperatures and atmospheric pressure determines the specifics of the winds, the general circulation of the atmosphere. Above the equator, where the greatest heating of the land and water surface occurs, ascending air movements dominate.
Warm air that has risen above the equator, cooling somewhat, loses a large amount of moisture, which falls out in the form of tropical showers. Then, in the upper atmosphere, the air flows north and south, towards the tropics. These air currents are called anti-trade winds. Under the influence of the rotation of the earth in the northern hemisphere, the anti-trade winds deflect to the right, in the southern - to the left. Above latitudes 30-40 ° С (in the subtropics) the angle of their deflection is about 90 ° C, and they begin to move along the parallels. At these latitudes, air masses descend to the heated surface, where they are heated even more, and move away from the critical saturation point. Due to the fact that in the tropics the atmospheric pressure is high all year round, and at the equator, on the contrary, it is low, at the surface of the earth there is a constant movement of air masses (trade winds) from the subtropics to the equator. The formation of the relief of deserts occurs under the influence of wind and water erosion. Deserts are characterized by some of the same type of natural processes that are prerequisites for morphogenesis: erosion, water accumulation, blowing out and aeolian accumulation of sand masses. Deserts of the same geomorphological type and degree of aridity are characterized by the same relief forms. In the most widespread sandy deserts, these are bare mobile and fixed immovable deflationary-accumulative aeolian forms (dunes, ridges, hillocks, dunes, etc.), often combined with salt marshes; in denudation and mountain deserts - steep cliffs (chinks), outliers, dry streams, drainless basins, salt lakes, etc. Desert territories are located either next to young high mountain systems(Karakum and Kyzyl Kum, Central Asian deserts - Alashan and Ordos, South American deserts), or - with ancient mountains (Northern Sahara). In any landscape, one can find the interaction of natural elements, a chain of connections that create the necessary balance in geobiocenotic systems. In this case, the quantitative ratio of natural components can be different. The ability of geobiocenoses to maintain their functions on the verge of a critical, oppressed state and then restore the disturbed equilibrium is an important property of the geographic environment, meets the vital interests of the organic world and, ultimately, people. Desert is equally characterized by natural bonds, and balance, and the ability to maintain productivity with a changing ratio of natural elements. But the connections themselves and the critical point in the oppressed state of natural forces in the desert are thinner, more sensitive, more reactive. Excessive stress or disruption of connections quickly becomes an extreme condition, causing a natural disaster. Droughts, excessive moisture deficit in the air and soil, sandstorms, a sharp drop in the groundwater level, drying out of wells, changes in the chemical composition of well waters (their salinity, increased presence of hydrogen sulfide) and other, no less serious changes are dangerous for desert vegetation. In desert conditions, the ability to awaken the extreme forces of nature to action is easier than in other landscape. They are dangerous because of their irreversibility or very slow self-healing processes. Therefore, the ways and means of developing the natural resources of deserts, ways of adapting living organisms, including people, their settlement, the resulting relationships with local nature are not at all similar to those observed in other natural zones. Desertification - back side and an inevitable companion to the widespread agricultural and industrial uses of the desert's natural resources. Construction of roads, mining facilities, pipeline laying, etc. make significant changes to the fragile natural ecosystems of the desert. However, with the immediate implementation of appropriate reclamation work, the landscape is usually restored; when environmental protection measures are ignored, the imbalance of desert ecosystems reaches such a degree when desertification processes become irreversible. According to UN experts, 19% of the land is on the verge of desertification (a combination of physical-geographical and anthropogenic processes leading to the destruction of ecosystems in arid regions, degradation of all forms of organic life and, as a result, to a decrease in the natural and economic potential of these territories). CHAPTER 2. PHYSICAL AND GEOGRAPHICAL FEATURES OF THE DESERT OF AFRICA
.1 Sahara Desert
The Sahara, the world's largest desert, stretches across most North Africa covering 9 million square kilometers. In fact, the Sahara Desert occupies 30% of the entire African continent. It is the hottest and hottest place in the world with summer temperatures that often exceed 57 degrees Celsius. The desert receives an annual downpour and very powerful sandstorms that raise the sand 1000 meters in height and move the dunes. The Sahara is located on the territory of more than ten states (Egypt, Libya, Tunisia, Algeria, Morocco, Western Sahara, Mauritania, Mali, Niger, Chad, Sudan). The Sahara defies categorization within one type of desert, although the sandy-rocky type is predominant. There are many regions in the desert: Tenere, Greater Eastern Erg, Greater Western Erg, Tanezruft, Hamada al-Hamra, Erg-Igidi, Erg-Shesh, Arabian, Libyan, Nubian deserts. Its age is about 2.5 million years. In the Sahara, about 160 thousand mirages are observed annually. They are stable and wandering, vertical and horizontal. Even special maps of caravan routes have been compiled with an assessment of the places where mirages are usually observed. These maps show where wells, oases, palm groves, and mountain ranges appear. Some say that the Sahara Desert was much larger before the first ice age, and some say that the Sahara Desert appeared 4000 years ago. For example, German scientists, using the methods of computer modeling of the Earth's climate, found that the Sahara became a desert 4000 years ago. Ten thousand years ago, the largest desert in the world was covered with grass and low bushes, but then it got hotter in summer, and the rains almost stopped. Naturally, many ancient civilizations disappeared, and all living things left the Sahara. According to scientists from the Potsdam Institute for Climate Research, the transformation of the Sahara into a desert has become one of the most dramatic climatic events on Earth for the foreseeable millennia. Why is the climate so fickle? It turns out that the inclination of the Earth's axis to the Sun is gradually changing: about 9 thousand years ago it was 24.14 degrees, now it is 23.45 degrees. Today, the Earth comes closest to the Sun in January, ten thousand years ago - at the end of July. Subtle changes in the Earth's orbit around the Sun, amplified by interactions with the atmosphere, ocean and land, alter the climate beyond recognition. The Sahara climate is extraordinary. The wet factor is the wide location of the Sahara to the north and south of the Northern Tropic. This explains the fact that most of the desert is under the influence of the northeast trade wind throughout the year. An additional influence on the climate is exerted by the Atlas mountain barrier located in the north, stretching from west to east and preventing the bulk of the moist Mediterranean air from penetrating into the desert. In the south, from the side of the Gulf of Guinea, wet masses enter the Sahara without hindrance in summer, which, gradually drying out, reach its central parts. Extreme dryness of the air, a huge amount of moisture deficit and, accordingly, an extremely high evaporation rate are characteristic of the entire Sahara. According to the precipitation regime in the Sahara, three zones can be distinguished: northern, central and southern. In the northern zone, precipitation falls in winter and their amount does not exceed 200 mm per year. To the south, their number decreases, and in the central zone they fall out sporadically. Their average size does not exceed 20 mm. Sometimes for 2-3 years there is no precipitation at all. However, in such areas, rainstorms can unexpectedly occur, causing severe flooding. The aridity of the Sahara also changes in a latitudinal direction, from west to east. There is no heavy rainfall on the Atlantic coast, as the rare westerly winds are cooled by the Canary Current passing along the coast. Fogs are frequent here. At the tops of mountain ranges and highlands, the amount of precipitation increases slightly due to the condensation of water vapor. Sahara is distinguished high degree volatility. Its total annual value varies from 2500 to 5500 mm, which is more than 70 times higher than the amount of precipitation. The Sahara is characterized by high, one might say, record-holders of air temperatures. The average temperature of the coldest month - January in almost all of the Sahara does not drop below 10 ° C. The average July temperature in the central part of the desert is 35 ° C. In many parts of the Sahara temperatures are noted above 50 ° C. -15 ° C. On the plains, the temperature rarely drops to minus 5 ° C. Frosts are frequent in the mountains. The daily amplitudes of air temperatures are very large - up to 30 ° С, and on the soil surface - up to 70 ° С.In early summer in the north of the Sahara, hot sirocco winds blow, which come from the central part of the desert. Strong winds cause dust and sand storms, the wind speed during a storm reaches 50 m / s. Masses of sand and small stones rise into the air, which greatly affect people and animals. Storms arise as suddenly as they end, leaving behind clouds of slowly settling dry dusty "fog". Tornadoes are not uncommon in the Sahara. The Sahara Desert consists of one quarter of volcanic mountains, one quarter of sand, rock and gravel plains, and small areas of permanent vegetation. Vegetation includes shrubs, grasses and trees in the highlands and in the oases along the river beds. Some of the plants are well adapted to this climate and grow within three days of rain, and sow their seeds within two weeks thereafter. Only a small part of the Sahara Desert is fertile - these areas take moisture from underground rivers and oases. The animals in the Sahara Desert are mainly gerbils, long-legged hares, deer, weasels, baboons, jackals, sand foxes, mongooses, desert hedgehogs and over 300 bird species. 2.2 Namib Desert
Namib is a coastal desert in southwestern Africa. The area of Namib is over 100,000 sq. km. The desert stretches 1,900 km along the Atlantic coast from the city of Namibe in Angola, across the whole of Namibia (which got its name from the desert) to the mouth of the Ulyphants River in the Cape province of South Africa. From the ocean, it goes deep into the continent at a distance of 50 to 160 km to the foot of the inland plateau; in the south, it connects with the southwestern part of the Kalahari. The name "Namib" in the language of the Nama people means "a place where there is nothing." The Namib Desert is extremely dry (only 10-13 years of rainfall per year) and, with the exception of a few coastal cities, practically uninhabited. Namib is considered the most ancient desert in the world: desert or semi-desert conditions have existed here continuously for 80 million years, that is, the desert was formed during the time of the dinosaurs. As a result, several endemic species of plants and animals have arisen here, which are adapted to life in the local extremely hostile climate and are not found anywhere else in the world. The Namib Desert is influenced by the Benguela Current, due to which the climate in the Namib Desert is cool and dry. Annual precipitation is less than 100 mm with high humidity and relatively low air temperatures. A stepped plain, rising to 1000-1200 meters in the east, sandy and gravelly relief in the north, rocky in the south. Namib is crossed by temporary streams and transit rivers Orange and Kunene. In places of shallow groundwater, you can find acacia, milkweed, aloe. The endless sea of sand dunes goes deep into the mainland, to the dry heart of the Namib Desert. At first glance, very few animals and plants live in this dry climate, however, one has only to sprinkle the rain, and the desert suddenly wakes up, a bright and active life begins. Seeds and bulbs, long time buried in the sand, they suddenly sprout, dry valleys turn into meadows, and after the plants appear birds and animals. Finches and larks eat grass seeds, and buzzards feast on numerous insects. In some places, the desert can even feed a large desert antelope that feeds on young grass. But if in one year there is an explosion of life in the desert, then another year can give only lean vegetation, and there are few animals ready to scour the barren desert in search of food. The Namib Desert is so dry that the plants and animals living in it were forced to develop specific biological mechanisms that respond local conditions... One of the Welwichia plants is found only in the Namib Desert, mainly in its northern part, where sand dunes give way to a gravel plain. Welwitschia seems to be insensitive to drought; in a few waterless years, the tips of its reddish-brown leathery leaves may dry out, but the first drops of rain return them green color and give you the opportunity to grow. It can survive for several years on the reserves of water absorbed from the earth in a wetter year. Early in the day, lizards and beetles crawl out of their sandy burrows to survey the area and collect food before the temperature rises, pushing them back into the cool sand. A temperature of 66 C was recorded on the surface, too high for the active life of most creatures. For some animals, only a short period of time is available between the cold at night, when the temperature is too low for them, and the searing heat of the day, when most are forced to seek shelter. When nocturnal animals crawl out of their holes into the cool air, the desert turns into a haven for completely different creatures. The shore near the Great Sandy Sea is often shrouded in fog, caused by the encounter of the cold Bengal air current heading north from Antarctica and the warmer, wetter Atlantic winds digging small holes in the sand. Each year, for about 60 days, the fog is so dense that it is carried 80 km inland. On a land where it rains only occasionally, these fogs are the main source of water for some desert dwellers. Darkling beetles drink droplets of mist, condensing on their bodies, and other beetles to collect moisture. The bodily juices of these creatures provide the necessary moisture to predators of the saltpug and chameleon. Low, bush-like trees and dry grass manage to survive in the harsh conditions of these arid deserts. Notable and inanimate nature... The Namib Desert has the tallest dunes on Earth. Their height exceeds 300 meters. And the complexity of their structure has been attracting the attention of geologists for several decades. In the desert, important deposits of tungsten and uranium ores and diamonds. The waters of the Atlantic Ocean, washing the shores of the Namib sea, are extremely abundant in life; the coast of the desert attracts numerous seals, seabirds and even penguins, which, despite the African heat, nest on deserted shores and coastal islands. 2.3 Kalahari Desert
The Kalahari Desert is just part of the world's longest sand zone, which covers vast areas in 9 African countries: Gabon, Congo, Angola, Zambia and Zimbabwe (center), Botswana, Namibia and South Africa. The total area of these sands is approximately 2.5 million square meters. km, and their depth in some places reaches 100 meters. The Kalahari area is about 600 thousand square meters. km. The Kalahari climate is arid with a summer maximum precipitation and mild winters, with aridity increasing towards the southeast. Precipitation (up to 500 mm) is confined to the summer period (November - April), but their value varies considerably both in time and in area. The Kalahari Desert occupies a syneclise in the body of the African Platform, filled with continental Mesozoic, Cenozoic deposits formed as a result of the weathering of rocks inside the depression itself. Along its periphery, edge plateaus and mountains rise above the sandy plains. In the west, the Kalahari region lies at an altitude of 1500 m above sea level, and in the east - even higher; the lowest point of the desert is 840 m above sea level. The Kalahari surface is composed of Tertiary and Quaternary horizontally lying continental strata (Karoo layers) of sandstones, pebbles and breccias. Three formations are distinguished in this continental strata. The lower, or fireplace suite, is composed of sands, sandstones and pebbles; the middle formation - sands, silicified sandstones and chalcedony limestones of the Late Cretaceous age - lies unconformably on the fireplace suite and, in turn, is unconformably overlapped by a suite of ocher sands of the Late Tertiary age. Above, modern deposits with a thickness of 100-150 m occur, represented by ferruginous sandstones and pebbles, red sands of the "Kalakhara type" and medium-grained aeolian sands. The entire territory of the Kalahari is occupied by sand dunes, located, as a rule, in chains at a distance of 70-150 m from each other. The accumulation of longitudinal dunes - alab - is especially common in the vicinity of the Molopo and Kuruman rivers. There are several types of Kalahari sands. The most common red sands, which can vary in color from bright pink to red to almost brown, are due to the presence of iron oxides. The origin of the red sands is due to the long-term destruction of Tertiary sandstones. Their grains are angular or round, mostly quartz, chalcedony, or siliceous; there are also mica and heavy minerals - granite, tourmaline, zircon, etc. The sands are mostly fine-grained. The grain size is most often 0, 15-0, 4 mm; fine sand fraction is 30-65%. The red dunes are often referred to as the "red toes" of the Kalahari. The Paleogene sandstones, when weathered during the Miocene arid period or even earlier, formed strata of light sands due to their covering with a calcareous shell. These sands are known as the Kalahari Sands. They are also available in Zambia, Congo, South Africa. It is believed that the Kalahari sands were carried by strong south-westerly winds from the Namib desert, on the other hand, it is more likely that a significant part of the aeolian sands was formed in the process of scattering the ancient alluvium of the now dry rivers Molopo and Noosob and their tributaries. It is quite obvious that in the Quaternary time these rivers were abounding in water and brought a significant amount of loose material, which occupied a vast area. The presence of "singing sands" is characteristic of the Kalahari. The closedness of the Kalahari Basin determined the nature of the runoff. The transit rivers and temporary streams draining it are directed towards the center of the depression. The largest of these are Noosob, Molopo and Avob. Their valleys are cut by several dry channels - omuram-bami; some of them fill with water during the rainy season. Valley of the r. Noosob is up to 3 km wide. The alluvial sediments of the rivers are heavily sandy. Therefore, rather thick accumulations of aeolian sands are common here in the form of parallel rows of dunes (dune chains) stretching for tens of kilometers (their height is up to 15 m) with a general orientation from northwest to southeast. The average height of the ridges above the inter-barkhan depressions is about 8 m (the maximum is up to 300 m). The average distance between the chains (from ridge to ridge) is about 225 m (the minimum is about 35.5 m, the maximum is 460 m). The climate of the Kalahari Desert is arid with a summer maximum precipitation and mild winters, with aridity increasing towards the southeast. Precipitation (up to 500 mm) is confined to the summer period (November - April), but their value varies considerably both in time and in area. Local variability plays an important role in the recovery of drought-affected vegetation. Average droughts are typical once every 3-5 years, severe - once every 10 years. The Kalahari is one of the hottest regions in South Africa. The average maximum temperature is plus 29 °, and the average minimum temperature is plus 12 °, the volatility is 3 thousand mm. In general, mild winters can sometimes be characterized by severe frosts. The desert wind regime in the basin of the Molopo and Nosob rivers is characterized by the constant dominance of northwestern winds. Because of this, the sands move forward to the southeast. The soils are mainly red-brown and orange-brown, sandy, structureless, consisting mainly of coarse and fine sand, weakly acidic, with low fertility, due to a lack of nitrogen and phosphorus. With depth, the color in more humid regions changes to yellow-brown, the sand becomes compacted. With close bedding of dense rock, a carbonate horizon appears in the lower part of the soil profile, where silicified deposits are found. The soil-forming process is similar to that of geologically ancient materials in Australia. The soils of vast depressions - pens are powerful, consist of eluvium of fine texture, non-saline, with a high content of organic matter in the north, but saline in the southern regions. Light texture, good water permeability of soils and the presence of close water confinement contribute to a more complete use of scarce sediments. Reminiscent of geographic location, relief, geological structure and history of the development of the Sahara, the Kalahari Desert has a fairly developed continuous, in places quite dense vegetation cover, thus it is more likely to resemble a deserted steppe or a deserted dry low grass savanna. This is especially pronounced north of 22 ° S. NS. Despite the fact that the locals called this area “the land of thirst,” grass stands here all year round and tree plantations grow, and after the rainy season (from December to March) ephemerals grow violently. South of 22 ° S NS. to r. Orange Kalahari takes on the character of a real desert: light rain falls rarely in summer, providing life for the scattered small trees, shrubs and sometimes, in wet years, summer grasses. Kalahari is one of the mysterious, inexplicable, intriguing and at the same time fascinating corners of the planet. The first riddle - how could a desert arise on the ocean coast? The second riddle - how is such biological diversity possible in this lifeless place? And there are hundreds of such riddles. Only the desert carefully keeps its secrets hidden under the thickness of the sand. Thus, the following can be said about the Kalahari: The Kalahari is one of the driest places on the planet, a land of fantastic landscapes and a unique animal world, an amazing place where you can observe how different kinds flora and fauna adapt to the harsh conditions of the desert, with an appearance reminiscent of the surface of the moon. 2.4 Karoo Desert
Karoo is an arid region in southern Africa, combining semi-desert plateaus and intermontane depressions south of the Bolshoy Ustup ridge and the Orange River valley. Usually, two main parts are distinguished with different topography and climatic conditions: the Big Karoo in the north, which is a depression between the Cape Mountains and the Big Ledge, and the Small Karoo in the south, a valley in Cape Mountains. Sometimes the Upper Karoo is also distinguished - a separate physical and geographical region, which is part of the wider South African plateau. The region is located mainly on the territory of the Republic of South Africa, as well as the adjacent areas of Namibia. Its total area is about 395 thousand square meters. km, that is, about a third of the entire territory of South Africa. The name Karru is of Khoisan origin which means dry or sterile. The semi-desert Karoo region is located in southern Africa north of about 34 ° S. NS. and west of 27 ° E. e. In the north-west in the region of 27 ° S. NS. the semi-desert abuts the coastal zone and plateau in the south of Namibia, which in turn becomes the Namib Desert. To the east, the Karoo is bordered by the Kalahari Desert. The region's aridity, which stands out against the mild Mediterranean climate in the east, is influenced by several main factors. The high-pressure belt in the Tropic of Capricorn evaporates moisture and transports it north towards the equator, where heavy rainfall falls. From the south, the advance of rain clouds is impeded by the Cape Mountains, from the north by the Great Ledge ridge. The cold Bengal Current along the southwest coast cools temperatures and also contributes to a drier climate. The flow of moisture into the region, primarily in the areas of the Little Karoo, is associated with advection (horizontal movement of air) from the warm Indian Ocean. The least arid part of the region, Malé Karoo, is a deep valley in the Cape Mountains between the Langeberg ranges in the south and Svartberg in the north at an altitude of 300-600 m above sea level. The valley is 245 km long, with an average width of about 48 km. Annual precipitation ranges from 400 mm on the slopes of the mountains to 130 mm on the bottom of the valleys. Big Karoo with an area of over 400 sq. km, located north of Malye, is a typical semi-desert with corresponding flora and fauna. Geologically, this is an erosion depression about 250 million years old, a place where rivers flow from the peaks of the Big Ledge. In the direction of the rivers, two basins are distinguished - western and eastern, the first of which is 225 km long and 80 km wide, the second 480 km long and 130-80 km wide. The average amount of precipitation is gradually decreasing from east to west - from 400 mm at the eastern border to 100 mm at the western one. The average elevation of the Big Karoo is 450-750 m above sea level. [The Upper Karoo is usually regarded as component South African plateau, is a plateau at an altitude of 1000-1300 m between the Orange River and the Big Ledge. Thus, the deserts of Africa are extremely heterogeneous in appearance, environmental conditions, the history of the formation of the organic world and, accordingly, in the composition of the organisms inhabiting them. Part of the arid territories lies in subtropical latitudes. A common feature of the climates of all African deserts is poor moisture throughout the year with sufficient heat supply. Showers are irregular, although there is a season of 1–2 months when they usually fall in the form of short showers. There may be no precipitation in the center for several years. Poor moisture is accompanied by high temperatures. Their large daily amplitude is characteristic - in the morning on the desert heights and in the subtropics there may be frosts. CHAPTER 3. THE IMPORTANCE OF THE AFRICAN DESERT AND ENVIRONMENTAL PROBLEMS
.1 Human use of deserts desert climate dune suite The main use of deserts is grazing livestock (camels, fine-wool sheep breeding); farming of drought-resistant crops is possible only in oases<#"justify">CONCLUSION
Africa is the oldest continent of our planet, the cradle of civilization. Despite its venerable age, more than 270 million years, this continent, washed by oceans, is perhaps the only one that has preserved harmony with nature and has not been subjected to the destructive influence of human activity. It is this, as well as the beauty of its nature and the stormy diversity and uniqueness of the animal world, that Africa is so attractive for study, research and tourism. The desert is distinguished by great natural contrasts, abrupt transitions from favorable natural conditions to unfavorable, sometimes difficult situation, which puts people in the face of serious consequences. These circumstances and the continuous territorial growth of the desert, the deterioration of the natural situation directly in the desert due to the growth of massifs of waving sands, a decrease in the forage capacity of pastures, salinization of irrigated lands and underground waters, an increase in dryness of years, etc. - all this makes it necessary to resist harmful to health and life of people to natural phenomena, to neutralize them. Currently, there is a tendency to expand the territories of a number of the largest deserts. So, the southern border of the Sahara in last years moves south on average 15 kilometers annually. Agricultural lands are often subjected to desertification, which causes significant damage to the economies of countries whose territory is directly adjacent to deserts. The reasons for this phenomenon are poor irrigation, irrational use of pastures, and too intensive farming. Deserts are the source of dust storms. A huge amount of dust and sand is carried by powerful air currents over considerable distances, and then thrown onto the ground, covering the soil layer with sand and contributing to land desertification. The problem has taken on a global character, as evidenced by the fact that, at the initiative of the UN, a special commission was created to study the problem and develop a targeted program of ways to solve it. The targeted program for the prevention of desertification includes a comprehensive economic study of deserts, their protection, as well as a system of measures to prevent their expansion. LIST OF SOURCES
1.Africa in the modern world / Authors: Deich T.L., Shubin V.G., Fituni L.L. and others - M., 2001 .-- 244 p. 2.Africa: ecological crisis and problems of survival. / Resp. ed. Potemkin Yu.V., Ksenofontova N.A. - M., 2001.255 s. .Wiegand V.K. Africa. National wealth and international redistribution of resources / Otv. ed. Fituni L.L. - M., 2004 .-- 147 p. .Gerasimchuk I.V. International environmental cooperation in southern Africa / Resp. ed. Potemkin Yu.V. - M., 2003, - 124 p. .Gusarov V.I. Sharpening the ecological problems of Africa // Kraєznavstvo. Geography. Tourism №29-32 P.12-14. .Dmitriev Alexey Scarlet carpet on the sand // Around the world №9 2010 P.32-35. .Morozova I. Wastelands of Africa // Kraєnavstvo. Geography. Tourism №44 P.21-23. .Petrov M.P. Deserts of the globe. M., 1973. .# "justify">. # "justify">. # "justify">. # "justify">. # "justify">. # "justify">. http://nature.1001chudo.ru/namibia_2420.html
In and and between and the desert in the tropical zone.
Semi-deserts are formed in conditions. What they all have in common is a long and hot warm period (average temperature 20-25 ° C, and in the tropics up to 30 ° C), strong evaporation, which is 3-5 times the amount (100-300 mm per year), weak surface, inland waters are poorly developed, there are many dry channels, vegetation is not closed.
Despite the common features inherent in all semi-deserts, they also have many differences.
1. Temperate semi-deserts they stretch in a wide strip (up to 500 km) from the western part of the Caspian lowland, through, to the East. In the Northern and semi-deserts, they occur in shorter ruptured areas in the interior and foothills. They differ from semi-deserts located in the tropical and subtropical zones in cold winters (down to -20 ° С). here they are light chestnut, which brings them closer to the steppe, and brown desert, often saline. If you move south along the semi-deserts of the temperate zone, you will notice that the signs of the steppes are fading away and the features of the deserts are increasing. There are also steppe feather grass and fescue, but among them you can already see wormwood and saltwort. Of the animals, there are saigas and turtles, snakes and lizards are more common.
2. Semi-deserts of the subtropical belt.
They are mainly located in the transitional part from deserts to mountain steppes in the form of a high-altitude zone in the inland parts and the Andes of America, in western Asia, and especially widely in. The soils are gravelly, gray-brown and gray soils. Cereals and various types of shrubs, a wide variety of cacti are common here. Rodents, snakes, lizards prevail from the animal world.
These are deserted savannas. They outline both inland and oceanic deserts - in Africa and, in South America, the north of the Atacama and the northwest of the Brazilian Highlands, in Asia and Australia.
The soils are thin, red-brown. The temperature in tropical semi-deserts, even in the coldest months, does not drop below + 10 ° С, and in summer it rises to 35 ° С. It rarely rains here. Precipitation is not more than 200 mm per year. With a lack of moisture, the bark is very thin. waters in tropical deserts are very deep and can be partially saline.
In such conditions, only plants that can tolerate overheating and dehydration can live. They have a deep, branched root system, small narrow leaves or thorns; in some plants, the leaves are pubescent or covered with a waxy coating, which protects them from the sun's rays. These include tree grasses, agaves, cactus, sandy acacias.